Expansion joints which utilize a flexible material to couple portions of a system together are used in a wide variety of applications to allow relative expansion and movement, due to temperature variations, of gas or liquid transport mechanisms such as pipes, ducts and other components which produce or receive the air or liquid. For example, in electrical power plants which utilize gas turbines to generate electrical power, expansion joints are used to connect portions of the ducts which transport the exhaust gas generated by the gas turbine. When operation of the gas turbine is initiated, the temperature of the ducts transporting the exhaust gas can rise from ambient temperature to approximately 1000 degrees farenheit in less than a minute. The high rate at which the temperature rises causes rapid and large variations in the temperature of different portions of the ducting system, including the expansion joint. As will be appreciated by those skilled in the art, such rapid differences in temperature in the components of the ducting system imposes a great deal of stress, also known as thermal shock, on all components of the ducting system and other operative portions of the power generation system.
U.S. Pat. No. 4,848,803 entitled Fabric Expansion Joints for Exhaust Systems of Gas Turbines describes an expansion joint which attempts to minimize the thermal shock by utilizing a U-shaped channel in the expansion joint to improve thermal distribution within the joint.
Although the U-shaped channel shown in the above referenced patent improves the thermal distribution within the joint, the discontinuity in the surface of the joint presented by the walls of the U-shaped joint which are perpendicular to the air flow path through the joint, restricts optimal heat distribution through the joint. As a result, the joint continues to be exposed to a high degree of stress, thus reducing the useful life of the joint.
If an expansion joint fractures in a system such as a power generation plant, the power generation mechanism generally has to be shut down while the repair to the expansion joint is made. Large costs are incurred by shutting down the power generation mechanism while the necessary repairs are made. Moreover, a fracture in an expansion joint can cause extremely hot gases to leak out of the ducting system, thus posing a threat to persons who may happen to be in the vicinity of the joint.
It is accordingly, a primary object of the present invention to provide an expansion joint which employs mechanisms which reduce the thermal stress placed on the joint, thus increasing the reliability of the joint.
It is a further, more specific, object of the present invention to provide an expansion joint with a channel which has walls which are sloped at an acute angle with respect to the direction of air flow through the joint, the sloped walls improving the thermal distribution within the joint, thus reducing the stress placed upon the joint, and also providing a geometry which is more tolerant to thermal distortion.
It is an additional object of the present invention to provide an expansion joint with an improved mechanism for clamping the flexible material of the expansion joint to a frame of the joint in order to obtain improved performance of the flexible material when the frame of the expansion joint is subjected to rapid temperature fluctuations.